Effective December 1987 and January 1988, the maximum speed limit on rural limited-access highways in Michigan was raised from 55 mph to 65 mph. This study examined the effects of the raised limit on traffic crashes, injuries, and deaths. A multiple time-series design was used, comparing roads where the speed limit was raised with roads where the limit remained unchanged. Data were collected on the numbers and rates of crashes, injuries, and deaths from January 1978 through December 1988. Times series intervention analyses were conducted to estimate effects associated with the speed limit change while controlling for long-term trends, cycles, and other patterns. Statistical controls were also included for major factors known to influence crash and injury rates in the state. Results revealed significant increases in casualties on roads where the speed limit was raised: 19.2% increase in fatalities; 39.8% increase in serious (A-level) injuries; and 25.4% increase in moderate (B-level) injuries. In addition, property-damage-only crashes increased 38.4%. Fatalities increased 38.4% on 55 mph limited-access freeways, suggesting that the 65 mph limit may have spillover effects on segments of freeways where the limit was not changed. The increased convenience of reduced travel time with the higher speed limit is obtained at a significant cost in terms of crash injuries and death.

  • Corporate Authors:

    University of Michigan Transportation Research Institute

    2901 Baxter Road
    Ann Arbor, MI  United States  48109-2150
  • Authors:
    • Wagenaar, A C
    • Streff, F M
    • Schultz, R H
  • Publication Date: 1989-12

Media Info

  • Features: Appendices; Figures; References; Tables;
  • Pagination: 76 p.

Subject/Index Terms

Filing Info

  • Accession Number: 00497334
  • Record Type: Publication
  • Report/Paper Numbers: UMTRI-89-28, HS-040 723
  • Contract Numbers: MPT-89-001A
  • Files: HSL, TRIS
  • Created Date: Sep 30 1990 12:00AM